RFR: 8294115: JNI local refs exceeds capacity warning in NetworkInterface::getAll

[Daniel Jeliński]

Please review this patch that fixes the warning `JNI local refs ... exceeds capacity` on Windows machines running with IPv6 stack enabled.

This case was missed in JDK-8187450 / #2963.

I verified that with this patch applied, the warning does not appear on a machine with 60+ interfaces. Tier2 also passes.

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Commit messages:
 - Clean up local references early

Changes: https://git.openjdk.org/jdk/pull/10377/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10377&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8294115
  Stats: 10 lines in 1 file changed: 10 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/10377.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10377/head:pull/10377

PR: https://git.openjdk.org/jdk/pull/10377